1. Field
This application concerns human expiratory airflow measurement and monitoring through the use of portable devices and systems.
2. Prior Art
Spirometers—devices that monitor respiration—are used in range of clinical, domestic, and vocational situations. Spirometers are used to diagnose and monitor common respiratory conditions such as asthma and chronic obstructive pulmonary disease (COPD), screen for occupational health hazards such as silicosis and black lung disease, and assist athletes and lung transplant recipients to monitor lung performance.
There are two general categories of spirometers—diagnostic spirometers and monitoring spirometers—each with its own set of requirements. Diagnostic spirometers are used in clinical settings, and must measure a number of respiratory parameters with high accuracy and precision. Monitoring spirometers are more frequently used in domestic and vocational settings; they must be cost-effective for individual users, compact, convenient, robust, low-maintenance, and designed for routine use.
Monitoring spirometers typically measure a person's peak expiratory flow rate (PEF, or PEFR), defined as the maximum volumetric airflow rate recorded during a voluntary forced expiration of air from the lungs. In addition to PEFR, another parameter measured by some monitoring spirometers is one-second forced expiratory volume (FEV1): the volume of air a person can forcibly exhale over the course of one second following a deep inhalation. (The subscript in this abbreviation indicates the duration of exhalation, in seconds.) Portable, compact monitoring spirometers that enable a user to monitor peak expiratory flow rate are commonly referred to as “peak flow monitors”. Peak flow monitors that facilitate measurement of peak expiratory flow are commonly referred to as “peak flow meters”.
Peak flow meters hold particular promise in the domain of asthma management. Asthma's prevalence world-wide has increased by approximately 50% per decade in recent history, and according to the World Health Organization (WHO), the human and economic burden associated with asthma surpasses that of AIDS and tuberculosis combined (2006). Approximately 300 million people world-wide suffer from asthma, and each year asthma results in over 200,000 deaths (International Union against Tuberculosis and Lung Disease, 2005). In America alone, asthma affects 20 million people, and accounts for $14 billion in health expenditures and lost productivity each year. Asthma is the most common chronic illness among children (National Institute of Health, 2006).
Asthma is a considerable problem, and peak flow meters play a role in the asthma management strategies that physicians and medical institutions recommend. According to the National Institute of Health (NIH): “A peak flow meter can tell you when an episode is coming—even before you feel the symptoms. Taking medicine before you feel symptoms can stop the episode. People over the age of 4 with moderate or severe asthma should use a peak flow meter at least daily” (NIH Publication No. 91-2664). The “Pocket Guide to Asthma Management” (2004) published by the Global Initiative for Asthma (GINA) recommends that patients monitor peak flow “as much as possible”. The National Asthma Education Program's (NAEP) 2007 Expert Panel Report highlights the value of regular PEFR readings in evaluating medications, detecting “early warning” signs, and precluding hospital visits (NIH Publication No. 07-4051). The American Thoracic Society (ATS) and National Heart, Lung and Blood Institute (NHLBI) recommend that patients with known respiratory disease regularly monitor their lung function. When a patient is able to routinely monitor his/her condition, the chances of successful management are improved.
Despite the recommendations of medical authorities, use of peak flow meters is far from ubiquitous. According to Allan H. Goroll, M D and Albert G. Mulley, M D, authors of the 2009 edition of “Primary Care Medicine”, only 20% of asthma patients who stand to benefit from using a peak flow meter actually use one. In practice, availability, adoption and adherence all strongly influence the impact that existing monitoring solutions have on asthma management outcomes worldwide.
While leading physicians and medical institutions are encouraging self-care through routine peak airflow monitoring, they are not recommending that the entire burden of asthma management fall on the shoulders of individual patients. Rather, medical authorities such as the NAEP are advocating for a network-based approach to self-care, characterized by collaborative relationships between patients, physicians and family members. Within such a network-based approach, the timely sharing of health information among concerned parties is of particular importance.
There are several classes of peak flow monitoring devices. One early type of device renders a threshold expiratory airflow perceptible to end-users by means of a whistle. If the whistle sounds when the user blows into the device, the user is meant to conclude that their peak airflow is above this threshold airflow rate. The threshold can be adjusted, usually by enlarging or contracting a leak orifice situated between a mouthpiece and the whistle section of the device. The leak orifice diverts a portion of incoming airflow so that this portion does not pass through the whistle. While such devices are inexpensive, simple to use, and reward their users sonically for exhaling as forcefully as possible, their threshold values must be set properly prior to use in order to achieve valid results. Furthermore, as threshold devices, they do not facilitate routine measurement in the manner that leading physicians and medical institutions now recommend.
The majority of peak flow meters currently available are mechanical devices with an enclosed moving element (such as a piston) connected to an externally visible pointer, positioned in close relation to a measurement scale. When a user blows into such a device, the force of his/her breath repositions the moving element, and its associated pointer points to a location on the measurement scale to indicate the user's peak expiratory flow. While such mechanical peak flow meters are simple and relatively inexpensive, friction, inertia, gravity, and other artifacts of mechanical implementation can compromise their accuracy. The need for at least one enclosed moving part has implications for reliability, ease of cleaning, and ease of sterilization. Since mechanical peak flow meters typically only display the result of the most recent measurement trial, they do not facilitate presentation of multiple trial results simultaneously—much less the visualization or exploration of trial data over a range of time scales.
In response to some of the limitations of threshold-whistle monitors and mechanical peak flow meters, electronic peak flow meters have been devised. Electronic peak flow meters typically incorporate some form of sensor, microprocessor, non-volatile memory and an LCD display. Approaches to sensing vary; some devices sense the rate at which a rotor spins in response to breath-generated airflow. Other devices sense a difference in pressure between two points along an air passageway, or the extent of Doppler shift in an ultrasound signal as it passes across an air passageway. Sensed values are usually translated into peak airflow rate values by a microprocessor, stored in non-volatile memory, and presented on an LCD display for a user to view. Electronic peak flow meters tend to be more accurate than their mechanical counterparts, and are able to store and display measurements (in some cases, FEV1 in addition to PEFR) from multiple trials. Some electronic peak flow meters also have the capability of sending measurement data to a personal computer via an attached cable or a wireless (radio-wave based) connection.
Although electronic peak flow meters typically offer greater measurement accuracy than mechanical peak flow meters, this accuracy comes at a price. Electronic peak flow meters tend to be significantly more expensive, and are also frequently less intuitive to use. To keep manufacturing costs down, user interface elements (buttons and LCD display symbols, symbol-sections and or pixels) are usually kept to a minimum—a factor that restricts ease of use. The electronic communication capabilities that some electronic peak flow meters offer are basic, and typically only possible with significant additional expense in the form of data cables, memory cards and personal computer software. Significantly, electronic peak flow meters do little at present to capitalize on advantages that software applications can provide within mobile contexts of use.
Electronic peak flow meters currently require batteries, and can run out of energy at inopportune moments—further eroding ease of use and reliability. The need for battery-powered electronics restricts how easily electronic peak flow meters can be washed and sterilized without risk of damage. While electronic peak flow meters are frequently sufficiently portable, they can become yet another battery-powered electronic device a patient must carry around on their person. In comparison with alternatives, electronic peak flow meters are more complex to manufacture and more difficult to recycle. They regularly contain toxic materials incongruous with their function as health-monitoring devices.
One interesting class of airflow sensor that has only been cursorily explored in the context of spirometry so far is that of the vortex whistle. Vortex whistles have the property that the fundamental frequency of sound waves they emit varies reliably and repeatably with the rate of fluid flow passing through them. This property makes it possible to derive a vortex whistle's through-passing airflow rate from its frequency emissions. Vortex whistles were first characterized by Bernard Vonnegut at General Electric Research Laboratory during the 1950s, and their principle of operation explained within his 1954 article “A Vortex Whistle”, published by the Journal of the Acoustic Society of America (Volume 26, Number 1). Essentially, a vortex whistle channels flowing fluid (liquid or gas) into a swirling vortex, and then through an outlet tube. As the vortex exits the outlet tube, it becomes unstable, and whips around with an angular velocity comparable to its rotational velocity. It is believed that the instability of the vortex as it exits the outlet tube creates the vortex whistle's sound.
To date, vortex whistles have been used primarily within the domain of industrial process control. The present research has uncovered one effort to apply the principle of the vortex whistle within the domain of spirometery, documented in “Application of the Vortex Whistle to the Spirometer” by Hiroshi Sato, et al. in Japan's 1999 Transactions of the Society of Instrument and Control Engineers. This effort employed a vortex whistle based on Vonnegut's design to measure expiratory airflow rate on a desktop computer equipped with a microphone. While this investigation introduced the use of a vortex whistle for measurement of expiratory airflow rate, it did not address how the design of a vortex whistle could be refined for use within the context of a portable monitoring spirometry solution, nor did it consider or address mobile scenarios of use.
In addition to vortex flow whistles, other forms of fluidic oscillators/fluidic whistles (devices that generate accoustic oscillation solely through their static structure and fluid dynamic interactions) have been considered within the context of spirometry, as evident from U.S. Pat. No. 3,714,828 (1973), U.S. Pat. No. 4,182,172 (1980), U.S. Pat. No. 7,0940,208 (2006), and U.S. Pat. No. 7,383,740 (2008). The spirometry solutions put forward by these patents share the advantage of minimal need for calibration. Because, however, these solutions employ fluidic oscillators as components within or attached to dedicated electronic peak flow measurement devices or systems, they suffer from many of the previously discussed limitations that are typical of electronic peak flow meters. Furthermore, the solutions presented within these patents do not capitalize on audio feedback as a means to reward a user for exhaling as forcefully as possible.
While a range of monitoring spirometry solutions exists, there remains significant room for improvement, particularly in the following areas:                Communication: At present, peak flow meters are predominantly stand-alone devices that do little or nothing to support timely, convenient flow of health information throughout a patient's network of family members and physicians. In an age when networked mobile information services are commonplace, the lack of convenient mobile connectivity and structured channels of digital communication are notable shortcomings.        Visualization: Existing portable monitoring spirometry solutions frequently fail to provide concise graphical reports designed to facilitate quick, sound interpretation and effective medical treatment decisions. Furthermore, the user interfaces for existing portable monitoring solutions do little to support exploration of trends over multiple timescales.        Ease of Use: Existing monitoring solutions currently fail to minimize the inconvenience of routine monitoring regimens—not only for patients, but also for family members and physicians.        Annotation: Existing peak flow monitoring devices for the most part do not assist patients to supplement automated quantitative measurement with self-reported contextual details. The ability to annotate a trial record with information such as whether the trial was performed following medication, what medication(s) were used, and other information pertaining to the trial would be of value in subsequent reviews of trial data by patients, physicians and family members.        Motivation: Operation of a peak flow meter is effort-dependent. If a patient does not routinely exhale as forcefully as they are able, the most precise of measurement solutions cannot ensure accurate results. Contemporary solutions do little to reward the consistent effort required for routine expiratory airflow measurement—nor do they frame the activity of measurement in ways that invite enjoyment. Present solutions typically frame peak flow measurement as a task to be completed, when it could alternatively be framed as a game to be played, a competition to be won, or the price of admission for some other form of rewarding experience administered in periodic installments.        Social Acceptability: The aesthetic/industrial design of available peak flow monitoring devices is usually clinical and utilitarian; for the most part, available devices and systems cannot easily be construed as fun, cool, elegant or fashionable. If an asthma patient feels reluctant or embarrassed to carry, hold or use a monitoring solution, it is of little value to them.        Correlation: Identifying the factors that exacerbate symptoms is a significant aspect of asthma management. Existing portable peak flow monitoring solutions do little to help patients correlate their own lung function with a range of potentially relevant environmental variables, such as local pollen count and geographic location. The ability to facilitate correlation could be beneficial not only for patients and their networks, but also for public health and medical research institutions in their efforts to understand asthma on a larger scale.        Reminding: The vast majority of monitoring solutions do not provide patients with the option of configuring and activating automated reminders that could support the routine monitoring regimens that medical authorities recommend.        Although the frequently-competing constraints of low cost, accuracy and reliability have been considered in the past, these constraints have not historically been balanced in ways that leverage the mobile technologies that a growing number of people carry on their persons.        